No worries.I just find topics like this fascinating.
As a final note to emphasize the importance of knowing the nature of the function the data represents (touche Mattywoo2), consider this. A 3rd order polynomial can be fit exactly to 4 points (just like a 2nd order polynomial can be fit to 3 points). By choosing the answer we want for y = 700 (e.g. 55), we can construct a 3rd order polynomial that not only fits the first 3 data points, but yields whatever we want (within limits) for x corresponding to y = 700. In a sense this is no less valid than fitting a 2nd order polynomial to the 3 points and finding the value of x for y = 700, since we are arbitrarily choosing the fitting function anyway. It just highlights the caveat of extrapolating data w/o knowledge of the functional nature of the data points.
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